1. Field of the Invention
The invention relates to the field of control switches of the type used in control panels and switch stations in an industrial environment.
2. Description of the Prior Art
Industrial control switches are characterized by different kinds of operators. In a push button control such as disclosed in Nelson et al, U.S. Pat. No. 3,770,925 issued Nov. 6, 1973, a momentary operator normally provides switch actuation for a short time. In a selector switch, on the other hand, such as disclosed in Wanner, U.S. Pat. No. 3,770,926, issued Nov. 6, 1973, an operator is maintained in one of several selectable positions for a typically longer period.
From these basic control units, other types have been developed through the addition of a secondary circuit to light the switch operator. A push button, for example, may be either constantly lighted or may be the push-to-test type, wherein the operator is lighted upon the successful actuation of the primary switch contacts.
One particular class of industrial switches with these various types of operators must be rugged, reliable, and sealed against the intrusion of oil and other contaminants in the industrial environment. Prior devices of this type such as disclosed in U.S. Pat. Nos. 3,770,925 and 3,770,926 have relied on mechanical contacts that have been sealed within contact blocks coupled to the switch operators.
With the introduction of solid state, digital control equipment there is a need for improved sealed control switches with low-bounce contacts for switching at d-c logic signal levels such as 5 volts, 15 volts and 30 volts.
In the field of digital office equipment, touch-actuated switching panels have been developed to replace traditional key-operated panels. These newer panels commonly involve several thin sheets of an insulating material such as Mylar. A spacing sheet is used between two other sheets on which conductive areas have been formed by screen printing or other deposition processes. The spacing sheet contains openings to allow the conductive areas on the spaced apart sheets to contact one another when pushed together at the touch of an operator. Such pressure sensitive switching panels have their functional labels arranged in patterns and arrays resembling keyboards, yet such panels are flush with the surface of the control panel or equipment utilizing them. Such panels have the advantage of sealed contacts, but in an industrial environment lack the tactility or other form of feedback to the human operator that is provided by traditional industrial controls. Such membranes, touch-sensitive switching panels are by the nature of their construction more readily adapted to arrays and have not provided suitable individual switches that can be located apart from control panels.